diff --git a/canopen/pdo/base.py b/canopen/pdo/base.py
index 771ed5af..5bc78ab8 100644
--- a/canopen/pdo/base.py
+++ b/canopen/pdo/base.py
@@ -229,7 +229,8 @@ def __init__(self, pdo_node, com_record, map_array):
         self._task = None
 
     def __repr__(self) -> str:
-        return f"<{type(self).__qualname__} {self.name!r} at COB-ID 0x{self.cob_id:X}>"
+        cob = f"0x{self.cob_id:X}" if self.cob_id is not None else "Unassigned"
+        return f"<{type(self).__qualname__} {self.name!r} at COB-ID {cob}>"
 
     def __getitem_by_index(self, value):
         valid_values = []
@@ -492,7 +493,7 @@ def subscribe(self) -> None:
         associated with read() or save(), if the local PDO setup is
         known to match what's stored on the node.
         """
-        if self.enabled:
+        if self.enabled and self.cob_id is not None:
             logger.info("Subscribing to enabled PDO 0x%X on the network", self.cob_id)
             self.pdo_node.network.subscribe(self.cob_id, self.on_message)
 
@@ -540,6 +541,8 @@ def add_variable(
 
     def transmit(self) -> None:
         """Transmit the message once."""
+        if self.cob_id is None:
+            raise ValueError("A valid COB-ID has not been configured")
         self.pdo_node.network.send_message(self.cob_id, self.data)
 
     def start(self, period: Optional[float] = None) -> None:
@@ -559,6 +562,8 @@ def start(self, period: Optional[float] = None) -> None:
 
         if not self.period:
             raise ValueError("A valid transmission period has not been given")
+        if self.cob_id is None:
+            raise ValueError("A valid COB-ID has not been configured")
         logger.info("Starting %s with a period of %s seconds", self.name, self.period)
 
         self._task = self.pdo_node.network.send_periodic(
@@ -579,7 +584,7 @@ def remote_request(self) -> None:
         """Send a remote request for the transmit PDO.
         Silently ignore if not allowed.
         """
-        if self.enabled and self.rtr_allowed:
+        if self.enabled and self.rtr_allowed and self.cob_id is not None:
             self.pdo_node.network.send_message(self.cob_id, bytes(), remote=True)
 
     def wait_for_reception(self, timeout: float = 10) -> float: